Stent design with sheath attachment members

ABSTRACT

A stent is provided having attachment members for allowing attachment of a sheath or sheaths. Accordingly, a practitioner is able to selectively choose a desirable sheath, such as a polymeric sleeve, a biomaterial, or a natural blood vessel, at a point-of-use and attach it to the sheath. The attachment members may be bendable tabs and/or secondary support stents.

CROSS-REFERENCE TO RELATED APPLICATIONS:

This is a divisional application of application Ser. No. 09/974,653,filed Oct. 10, 2001, now U.S. Pat. No. 7,399,312, the entire content ofwhich is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to vascular stents and, more particularly, tocovered vascular stents.

2. Description of Related Technology

In the prior art, it is known to provide a covering for an implantablevascular stent, such as that disclosed in U.S. Pat. No. 5,916,264. Suchcovered stents or stent/grafts are used for a variety of vasculartreatments, but have particular usefulness in endovascular applicationsto support or maintain the patency of the natural vessel. Depending onthe particular needs of a patient, a specific stent/cover combination ischosen as a treatment. Generally, however, stent coverings are emplacedon the stent at a manufacturing facility. As a result, medicalpractitioners have been traditionally limited in their selection of astent and covering combination to what is commercially available.

To overcome some of the deficiencies of the prior art, mountable sheathsfor emplacement onto a stent have been developed which allow apractitioner to select a particular sheath and stent combination at apoint-of-use, beyond the manufacturing facility. A mountable sheath isdisclosed in WIPO International Publication No. WO 00/12147, theapplicant of which is the same as the assignee herein. The mountablesheath is slitted to facilitate mounting onto a stent, and may betreated with a pharmaceutical agent, radioactive agent, bioactive agent,or a combination thereof. The sheath is attached and retained on thestent using compressive force, glue, a protective sheath, or socks. Thecompressive force is generated radially (inwardly and/or outwardly), bythe sheath itself, the stent, or both. It is, however, desired toprovide a simplified method of attaching and retaining the mountablesheath, as well as other sheaths, to a stent.

SUMMARY OF THE INVENTION

The present invention provides a means for selecting and joining aparticular stent configuration and a particular covering or lining forthe stent to tailor the final stent/graft device to a particularpatient.

With the subject invention, a stent is provided having aradially-expandable body with axial ends, wherein at least one bendabletab extends from one of the ends. The tab is formed to be bendable so asto at least partially overlap the body upon being bent. Accordingly, asheath or cover can be concentrically arranged (internally and/orexternally) of the stent, with the tab being bent into engagement withthe sheath so as to provide a holding force therein.

In one aspect of the invention, a tubular stent is provided with aplurality of circumferentially spaced tabs extending from each end. Theconstruction of the stent may be of any configuration or material knownin the art.

It is preferred that the tabs be unitarily formed from or integral withthe stent, such as by being laser-cut from the same stock in forming thestent. In one embodiment of the invention, the tab is connected to thestent via a single stem which allows for relative easy bending thereof.To ensure low-risk of failure (i.e., tab separation from the stent), thestem may be strengthened by forming it thicker than the stent, usingknown metal-working processes, or by the application of a strengtheningagent, such as a coating, cladding, and the like. Alternatively, thestem may be formed thinner than the stent to enhance bendability of thetab. Furthermore, the tab is preferably formed with a non-linear shape(such as with a U-shape, V-shape, circle shape, box shape, triangularshape, rectangle shape, and so forth) so as to provide a distributedarea of contact force (as opposed to point contact or line contact) uponthe sheath, with the arms of the tab diverging to further enhance thiseffect. To ensure that the tabs maintain their bent sheath-engagementpositions during use, the tabs are preferably formed from a deformablematerial with little recoil or elasticity, such as stainless steel,tantalum, niobium, or a platinum-enhanced alloy.

The sheath may be formed from a polymer sleeve such as a PTFE, ePTFE,polyurethane, polypropylene, polyester or other biocompatible material.In another aspect of the invention, the polymer sleeve may be formed ofa biodegradable material. Bioactive or therapeutic agents, such as drugsor biological materials may be incorporated in or on the polymericsleeve for release subsequent to implantation. The sleeve may also beformed from a biomaterial such as elastin or collagen, or from a sectionof natural blood vessel (e.g., saphenous vein). With the subjectinvention, a physician, or other practitioner, can selectively choosethe type of sheath required, as well as the type of pre-implantationtreatment thereof. For example, a physician may choose to soak apolymeric sleeve in a particular therapeutic agent prior toimplantation.

Once selected, the sheath may be fixed externally or internally of thestent, by disposing it concentrically therewith, and bending the tabsaccordingly to engage and secure the sheath to the stent. As analternative embodiment, multiple sheaths can be disposed internally orexternally of the stent, with the tabs holding the composite structurein place. Furthermore, one or more sheaths can be simultaneouslydisposed internally and externally of the stent, with a portion of thetabs being bent inwardly to provide holding force for the internalsheath(s) while a portion of the tabs are bent externally to provide aholding force for the external sheath(s).

A tool may be provided for bending the tabs in assisting a practitioner.

As a second embodiment of the subject invention, one or more secondarysupport stents may be utilized to hold the sheath or sheaths relative tothe stent. In one variation, a ring-shaped support stent, having a muchshorter axial length than the main stent, may be plastically deformed(e.g. by crimping) in proximity to an end of the main stent to providenecessary holding force for the sheath(s). One or more of such supportstents may be used internally and/or externally of the main stent, asrequired.

These and other features of the invention will be better understoodthrough a study of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side elevational view of a stent having bendable tabs formedin accordance with the subject invention;

FIG. 2 is an enlarged view of section 2 of FIG. 1;

FIG. 3 is an elevational view of the subject invention having a sheathdisposed about the body of the stent;

FIG. 4 is an end elevational view of the subject invention havingmultiple sheaths; and,

FIG. 5 is an elevational view of a second embodiment of the subjectinvention using crimped support stents.

DETAILED DESCRIPTION OF THE INVENTION

With the subject invention, a device and method are provided forallowing practitioners to selectively choose a sheath as a covering fora stent at a point-of-use. With this versatility, a practitioner has theability to utilize not only polymeric sheaths, but also biomaterial andnatural material, and allow for such to be treated prior toimplantation, such as soaking in a therapeutic agent. The subjectinvention may be used in the coronary vasculature, esophagus, trachea,colon, biliary tract, urinary tract, prostate and brain.

With reference to FIGS. 1-4, a first embodiment of the subject inventionis depicted, wherein a stent 10 is provided having a tubular body 12, afirst axial end 14, and a second axial end 16. One or more bendable tabs18 extend from the first and/or second axial ends 14, 16.

The stent 10 may be of any stent configuration known to those skilled inthe art, including those used alone or in a stent-graft arrangement.Various stent types and stent constructions may be employed in thepresent invention including, without limitation, self-expanding stentsand balloon expandable stents. The stents may be capable of radiallycontracting as well. Self-expanding stents include those that have aspring-like action which cause the stent to radially expand or stentswhich expand due to the memory properties of the stent material for aparticular configuration at a certain temperature. Other materials areof course contemplated, such as stainless steel, platinum, gold,titanium, tantalum, niobium, and other biocompatible materials, as wellas polymeric stents. The configuration of the stent may also be chosenfrom a host of geometries. For example, wire stents can be fastened in acontinuous helical pattern, with or without wave-like forms or zigzagsin the wire, to form a radially deformable stent. Individual rings orcircular members can be linked together such as by struts, sutures, orinterlacing or locking of the rings to form a tubular stent.

It is preferred that the stent 10 be of the type that is etched or cut(e.g., laser cut) from a unitary cylindrical stock. Accordingly, thetabs 18 desirably may be cut from the same stock as the tubular body 12and be formed unitarily therewith. Desirably, the tubular body 12 isradially-expandable using conventional techniques, such as balloondistension, or may be self-expanding.

With reference to FIG. 2, in one embodiment, the tabs 18 have agenerally U-shape with side legs 20 which slightly diverge. With thisstructural configuration, the tabs 18 may distribute holding force overan area, rather than have point contact or line contact (e.g., if asingle slender wire was to be used). The side legs 20 terminate in freeends 22 which are flared slightly outwardly from an open mouth 24 of thetab. It is desired to ensure that sharp edges are eliminated from thetabs 18, especially at the free ends 22 to prevent unintended punctureof the vessel. Because the tabs 18 may be located externally of animplanted stent, and in contact with a vein wall, it is desired toensure that micromovement of the tabs will not result in any abradingdamage to the vein wall. Advantageously, where the tabs 18 may beunitarily laser cut with the tubular body 12, electropolishing of theentire assembly removes all sharp edges.

It is preferred that the tabs 18 have a shape which imparts a holdingforce over an area, such as a v-shape, circle shape, box shape,triangular shape, rectangular shape and so forth with the tab 18 beingdefined by an element outlining the shape, or being at least partiallysolid across the area of the tab (e.g., a solid disc). It is preferredto use a configuration other than a slender linear shape so that, asmentioned above, holding force is distributed over an area. A flattenedor deformed wire may also distribute a holding force over an area.

The tab 18 is connected to the body 12 via a stem 26 which is bendable.With unitary manufacturing of the tabs 18 and the body 12, the stem 26will have the same thickness as other parts of the stent 10. It may bedesired, however, to strengthen the stem 26 so as to reduce thelikelihood of failure thereof which may result in separation of the tabs18 from the body 12. The stem 26 may be strengthened in a variety ofways, such as: by providing additional material therein to thicken it;using known metal-working techniques; and/or providing a strengtheningagent, such as a coating, cladding, or the like. The stem 26 is formedof sufficient length to allow the tab 18 to be bent thereabout to atleast partially overlap the body 12. Alternatively, it may be desired toform the stem 26 thinner than surrounding portions to enhance thebendability thereof. Also, the stem 26 may be thinned to increase itscross-sectional width so as to provide a holding force over a largerarea.

With reference to FIG. 3, the stent 10 is covered by a sheath 28 withthe tabs 18 extending from the assembly. As previously discussed, thesheath 28 may be formed from any number of materials, includingsynthetic or natural polymers, biomaterials, or natural materials, suchas natural blood vessel (e.g., a saphenous vein). The sheath 28 may havea tubular shape, or be slitted as shown in WIPO InternationalPublication No. WO 00/12147. The entire disclosure of WIPO InternationalPublication No. WO 00/12147 is incorporated herein by reference herein.

As shown in FIG. 3, the sheath is concentrically disposed relative tothe stent 10 (as shown in FIG. 3 disposed, for example, radiallyoutwardly) and one or more of the tabs 18 are caused to be bent intoengagement therewith. Accordingly, the sheath 18 is attached to thestent 10 and shall be retained relative thereto by the holding force ofthe tabs 18. It is desired to have the tabs 18 sufficiently bent so thatthe tabs 18 are recessed within, or flush with, the sheath 28.Accordingly, it is desirable that no portion of the tabs 18 shall extendoutwardly from the assembly.

To ensure that the tabs 18 maintain their bent positions afterapplication, the tabs 18 are preferably formed from a deformablematerial with little recoil or elasticity, such as stainless steel,tantalum, niobium, or a platinum-enhanced alloy. Shape memory alloys,such as nitinol, can be used so long as the tabs 18 are treated to notre-gain their original unbent shape once implanted.

With reference to FIG. 4, multiple sheaths 28 may be disposed externallyof the stent 10. Likewise, one or more of the sheaths 28 may be disposedradially inwardly of the stent 10, with one or more of the tabs 18 beingbent inwardly into engagement with the sheath(s) 28. As a furthervariation, one or more sheaths 28 may be simultaneously disposedinternally and externally of the stent 10, with a portion of the tabs 18being bent inwardly, and a portion of the tabs 18 being bent outwardly.

Because of the ability to apply the sheath 28 at the point-of-use, apractitioner may choose to treat the sheath 28 prior to implantation,such as soaking with one or more of the following therapeutic agents:anti-thrombogenic agents (such as heparin, heparin derivatives,urokinase, and PPack (dextrophenylalanine proline argininechloromethylketone); anti-proliferative agents (such as enoxaprin,angiopeptin, or monoclonal antibodies capable of blocking smooth musclecell proliferation, hirudin, and acetylsalicylic acid);anti-inflammatory agents (such as dexamethasone, prednisolone,corticosterone, budesonide, estrogen, sulfasalazine, and mesalamine);antineoplastic/antiproliferative/anti-miotic agents (such as paclitaxel,5-fluorouracil, cisplatin, vinblastine, vincristine, epothilones,endostatin, angiostatin and thymidine kinase inhibitors); anestheticagents (such as lidocaine, bupivacaine, and ropivacaine);anti-coagulants (such as D-Phe-Pro-Arg chloromethyl keton, an RGDpeptide-containing compound, heparin, antithrombin compounds, plateletreceptor antagonists, anti-thrombin antibodies, anti-platelet receptorantibodies, aspirin, prostaglandin inhibitors, platelet inhibitors andtick antiplatelet peptides); vascular cell growth promotors (such asgrowth factor inhibitors, growth factor receptor antagonists,transcriptional activators, and translational promotors); vascular cellgrowth inhibitors (such as growth factor inhibitors, growth factorreceptor antagonists, transcriptional repressors, translationalrepressors, replication inhibitors, inhibitory antibodies, antibodiesdirected against growth factors, bifunctional molecules consisting of agrowth factor and a cytotoxin, bifunctional molecules consisting of anantibody and a cytotoxin); cholesterol-lowering agents; vasodilatingagents; and agents which interfere with endogenous vascoactivemechanisms. In addition, radioactive agents and bioactive agents may beused in various combinations, along with the therapeutic agents listedabove.

The stent 10 may take any form, such as a “box car” type stent, whichutilizes discrete stent elements linked together by flexibleconnections, such as that shown in FIG. 5 of U.S. Pat. No. 5,693,085.The entire disclosure of U.S. Pat. No. 5,693,085 is incorporated byreference herein. With a “box car” stent, the tabs 18 will only extendfrom the end elements, and not the central stent elements. It is alsopossible to form the stent 10 with tabs extending only from one axialend 14, 16 of a tubular stent, and only one of the tabs 18 at therespective axial end 14, 16 may be required depending on the application(e.g., amount of holding force required). It is preferred to use aplurality of the tabs 18 with such tabs 18 being circumferentiallyevenly-spaced, such as with three tabs 18 at each axial end 14, 16located at intervals of 120 degrees relative to the circumference of thebody 12. In this manner, an even distribution of holding force can beachieved to ensure proper fixing of the sheath 28 to the stent 10.

Conventional techniques may be used to implant the stent 10/sheath 28assembly. As a further variation, one or more barbs 19 may be formed onone or more of the tabs 18 which are formed to puncture a surroundingvessel wall upon implantation of the assembly. The barbs 19 need only beformed on the side of the tabs 18 which will be externally exposed witha completed assembly, and preferably, are formed in proximity to thefree ends 22. The barbs 19 shall act to provide additional holding forcefor the structure at a desired location.

A hand tool (not shown) may also be provided to aid a practitioner inbending the tabs 18.

In a second embodiment of the invention, one or more ring-shaped supportstents 30 replace the tabs 18 to provide holding force for the sheath28. With reference to FIG. 5, the support stents 30 generate a relativepressing force with the stent 10 (hidden from view) to hold the sheath28 in place. As with the tabs 18, if shape memory alloys are used informing the support stents 30, it is desired to treat the support stents30 such that will prevent the support stents 30 from re-gaining theiroriginal shape. It is also desirable that no portion of the stent 10come into contact with the support stents 30.

In one variation, the support stents 30 may be plastically-deformed toprovide, and maintain, the necessary holding force. For example, thesupport stents 30 may be crimped. The support stents 30 may be partiallyplastically deformed, such at discrete points or along a region, or maybe wholly plastically deformed. Any plastic deformation of the supportstents 30 should not interfere with the ability of the stent 10 and thesheath 28 to be implanted (i.e., interfere with the ability to radiallycompress and radially expand). Alternatively, the support stents 30and/or the stent 10 may generate a radial pressing force which holds thesheath 28.

It is preferred that the support stents 30 be of limited axial lengthand not be coextensive with the body 12 of the stent 10. To avoid endseparation of the sheath 28 from the stent 10, the support stents 30 aredisposed in proximity to the axial ends 14, 16. It is possible to useonly one of the support stents 30, such as at the upstream axial end 14,16 of the stent 10 relative to blood flow. In addition, as shown indashed lines, it is possible to form at least one tab 18 at one axialend 14, 16 in connection with the use of one or more of the supportstents 30 to supplement the holding force thereof. As an alternative, asingle support stent 30 may be used which extends over a major extent ofthe sheath 28.

The support stents 30 may be of any construction known in the art. Thestructure may be plastically-deformable upon being crimped radiallyinwardly or outwardly.

As with the first embodiment, multiple sheaths 28 may be disposedinternally and/or externally, with the support stents 30 providingholding force intraluminally. If there is reliance on plasticdeformation of the support stents 30, the support stents 30 may becrimped radially outwardly to hold any internally-disposed sheaths 28.

To facilitate the plastic deformation of the support stents 30, a tool(not shown) may be provided.

Various changes and modifications can be made to the present invention.It is intended that all such changes and modifications come within thescope of the invention as set forth in the following claims.

What is claimed is:
 1. A stent comprising a radially-expandable bodyhaving first and second axial ends, and at least one bendable tabextending from said first axial end, each bendable tab comprising twofree ends, each bendable tab having a first configuration and a secondconfiguration, when the bendable tab is in the first configuration thetwo free ends of the bendable tab are directed in a first direction andwhen the bendable tab is in the second configuration the two free endsare directed in a second direction opposite the first direction, thebendable tab at least partially overlapping the body in the secondconfiguration; wherein said at least one tab is connected to said bodyvia a single bendable stem, the stem being straight when the bendabletab is in the first configuration, the stem having a bend when thebendable tab is in the second configuration.
 2. The stent as in claim 1,wherein said stent is generally cylindrical.
 3. The stent as in claim 1,wherein at least one bendable tab extends from said second axial end,said tab being bendable to at least partially overlap said body.
 4. Thestent as in claim 1, wherein a plurality of said tabs extend from saidfirst axial end.
 5. The stent as in claim 1, wherein said at least onetab has a non-linear shape.
 6. The stent as in claim 1, wherein said atleast one tab is unitarily formed with said body.
 7. The stent as inclaim 1, further comprising at least one barb extending from at leastone said tab.
 8. The stent as in claim 1, wherein said at least one tabhas a U or V shape with side legs terminating in the free ends formingan open mouth therebetween.
 9. The stent as in claim 8, wherein saidside legs of said tab diverge.
 10. The stent as in claim 8, wherein saidfree ends of said side legs are flared outwardly.
 11. The stent as inclaim 1, wherein said stem is strengthened to reduce likelihood offailure upon bending.
 12. The stent as in claim 1, wherein said stem isprovided with a strengthening agent, wherein the strengthening agent iseither a coating or a cladding.
 13. The stent as in claim 1, whereinsaid stem has a thinner profile than surrounding portions of the stentto facilitate enhanced bending.
 14. The stent as in claim 1, wherein thestent at said axial end has a ring of wave or zig-zag form, said stembeing integral with said ring at a valley of said wave or zig-zag formand extending until beyond the peaks of said wave of zig-zag form. 15.The stent as in claim 1, wherein one or more barbs are formed in saidtab.
 16. The stent of claim 1, further comprising a first sheath, thesheath being between the at least one bendable tab and the stent whenthe tab is in the second configuration.
 17. A stent comprising aradially-expandable body having first and second axial ends, and atleast one bendable tab extending from said first axial end, eachbendable tab comprising two free ends, each bendable tab having a firstconfiguration and a second configuration, when the bendable tab is inthe first configuration the two free ends of the bendable tab aredirected in a first direction and when the bendable tab is in the secondconfiguration the two free ends are directed in a second directionopposite the first direction, the bendable tab at least partiallyoverlapping the body in the second configuration wherein said tabgenerates a relative pressing force with said body to hold a sheath inplace, said sheath being not bonded to said tab with said pressing forcesolely acting to hold said sheath in place.
 18. A prosthesis comprising:a plurality of circumferential bands, one of the plurality ofcircumferential bands forming a first end of the prosthesis, another ofthe plurality of circumferential bands forming a second end of theprosthesis, the plurality of circumferential bands including firstcircumferential bands of a first wavelength, each first circumferentialband comprising: a plurality of first struts interconnected by aplurality of first turns directed towards a first end of the prosthesisand a plurality of second turns directed towards a second end of theprosthesis, each turn engaged to two of the plurality of first strutsforming a first unit of the first circumferential band, the first unithaving a first configuration; a plurality of tabs, each tab comprising aturn and two second struts, a first end of each second strut engaged tothe turn and a second end of each second strut being a free end, theturn and two second struts of the tab having a second configuration, thesecond configuration being the same as the first configuration of thefirst unit of the first circumferential band, each tab engaged to an endof the prosthesis; a first sheath, the first sheath engaged to theprosthesis by at least some of the plurality of tabs.
 19. The prosthesisof claim 18, the first unit having a size and the tab having a sizeequal to the size of the first unit.
 20. The prosthesis of claim 18, theplurality of tabs comprising three first tabs and three second tabs,each first tab engaged to the first end of the prosthesis and eachsecond tab engaged to the second end of the prosthesis.
 21. Theprosthesis of claim 18, each tab connected to the end of the stent by astem, the stem being engaged to the turn of the tab.
 22. The prosthesisof claim 18, the plurality of circumferential bands further comprisingsecond circumferential bands of a second wavelength, each secondcircumferential band comprising: a plurality of struts interconnected bya plurality of first turns directed towards a first end of theprosthesis and a plurality of second turns directed towards a second endof the prosthesis.
 23. The prosthesis of claim 22, the first and secondcircumferential bands alternating from the first end of the prosthesisto the second end of the prosthesis.
 24. The prosthesis of claim 23, onesecond circumferential band forming the first end of the prosthesis andanother second circumferential band forming the second end of theprosthesis.
 25. The prosthesis of claim 22, the second wavelength beingless than the first wavelength.
 26. The prosthesis of claim 18, whereinthe first sheath is radially adjacent to the plurality ofcircumferential bands and the first sheath is radially adjacent to theat least some of the plurality of tabs, the first sheath being betweenthe plurality of circumferential bands and the at least some of theplurality of tabs.